This invention relates to the production of proteins, and more particularly to a recycle process for the manufacture of proteins by the biochemical oxidation of gaseous hydrocarbons in the presence of a nitrogenous nutrient.
Proteins can be produced by the microbial conversion of hydrocarbons under fermentation conditions. In conducting such conversions a hydrocarbon is contacted in an aqueous medium containing a nitrogen source and other desired nutrients with an oxygen-containing gas. The protein produced in the reaction remains in the aqueous medium and unused oxygen and byproduct carbon dioxide are removed from the reaction as a gas phase. More recently, it has been discovered that greater protein yields are realized when the conversion is carried out using an enriched oxygen-containing gas; accordingly, later hydrocarbon conversion processes are conducted using oxygen-enriched air or high purity oxygen as the oxygen-containing gas.
Since the reaction occurs in the aqueous phase and the solubility of oxygen in water is relatively low, it is desirable to use excess oxygen-containing gas to effect reasonable conversion rates. When an oxygen-enriched gas or substantially pure oxygen is used as the oxygen source it is important for economic reasons to recover unused oxygen-enriched gas. Brugerolle et al. U.S. Pat. No. 3,833,477, discloses the separation of oxygen from water vapor and carbon dioxide contained in a gaseous effluent stream from an aerobic fermentor by cooling the gaseous effluent and condensing water vapor and carbon dioxide from the gaseous effluent. The separated oxygen can then be recycled to the fermentor. Sicar et al. U.S. Pat. No. 4,690,696 discloses the separation by pressure swing adsorption of oxygen from carbon dioxide in an organic substance fermentor effluent gas stream, and recycle of the recovered oxygen to the fermentor.
Harrison, "Making Protein from Methane", Chemtech, September, 1976, pp 570-574, and Klass et al., "Key Process Factors in the Microbial Conversion of Methane to Protein", Chemical Engineering Progress Symposium Series, No. 93, Vol. 65 (1969), pp 72-79 describe the metabolism of methane to protein concentrate by means of a methane utilizing microbe. There is no discussion of recovery of unused oxygen or methane in either of these articles. A continuous reaction process for converting methane to protein by the reaction of methane with oxygen and nutrients in the presence of methane-utilizing bacteria is disclosed in an article entitled "A Fairytale in Odense", appearing in Statoil Magazine, issue 90 2, pp 12-15.
More efficient and economical protein manufacturing processes are continuously sought. The efficiency and economics of hydrocarbon oxidation protein production processes could be considerably enhanced if both the excess oxygen and excess hydrocarbon from a gaseous hydrocarbon protein production plant could be safely recovered and recycled. The present process provides such an improvement.